1. Field of the Invention
The present invention relates to rack and pinion steering gear assemblies and rack bearings used therewith.
2. Description of the Related Art
Rack and pinion steering gear assemblies include an intermeshed pinion shaft and rack. A rack bearing is typically positioned to bear against the rack and bias it toward the pinion shaft to maintain the mesh clearance between the pinion shaft and rack. When a rack and pinion steering gear is assembled, the rack bearing is adjusted to provide a desired mesh clearance between the pinion gear and rack. During the initial period of use of the rack and pinion steering gear, typically referred to as the “break-in” period, the rack and pinion gears are subject to a rapid period of wear which can enlarge the mesh clearance between the pinion shaft and rack. The assembly, including the rack bearing, is also subject to wear over the full life of the steering gear. If the mesh clearance between the pinion shaft and rack becomes too large, it can lead to rattle noise and ultimately customer dissatisfaction and complaints. To address the wearing of the pinion shaft, rack and rack bearing and inhibit the development of rattle, a biasing assembly is typically employed to bias the rack bearing into engagement with the rack and various biasing assemblies for use the rack bearing have been developed.
FIG. 1 illustrates a conventional rack and pinion steering gear assembly 10. Steering gear assembly 10 includes a pinion shaft 12 that is intermeshed with rack 14. Pinion 12 and rack 14 are disposed within housing 16. Pinion shaft 12 is rotatably supported within housing 16 on opposite sides of rack 14 by bearings 18 and 20. A rack bearing 22 urges rack 14 into contact with pinion 12. Rack bearing 22 includes a slide lining 24 that is in direct contact with rack 14 and which can be used to reduce the frictional resistance to the relative sliding between rack 14 and rack bearing 22.
A spring 26 exerts a biasing force on rack bearing 22 urging it into contact with rack 14. Spring 26 is engaged with adjustment plug 28 on its end opposite rack bearing 22. A small clearance or compliance zone 30 is typically provided between plug 28 and rack bearing 22 to allow for limited movement of rack bearing 22 toward adjustment plug 28 due to tolerance variations on rack 14 and pinion 12. While zone 30 is often referred to as a clearance zone, because a load is being applied across zone 30 it is more properly referred to as a low load compliance zone. When assembling steering gear 10, adjustment plug 28 is installed to a predefined torque and then retracted a predefined magnitude, e.g., rotated a predefined minimal quantity, the pre-defined torque will correspond to a known load on the intermeshed gears of pinion 12 and rack 14 while the retraction of adjustment plug 28 provides for compliance zone 30. As the assembly wears, compliance zone 30 will grow in size and spring 26 will urge rack bearing 22 further away from plug 28 and the force exerted by spring 26 on rack 22 will decrease. As compliance zone 30 grows, the working range of spring 26 also increases and at some point the enlarged size of compliance zone 30 may cause gear rattle.
During initial assembly, if plug 28 is installed at too great a distance from rack 14, the working range of spring 26 will be undesirably large and rattle may result. If plug 28 is inserted to far into housing 16 during the initial assembly, the excessive force exerted by rack bearing 22 on rack 14 would undesirably increase the resistance to steering efforts exerted by the driver of the vehicle.
Another example of a biasing assembly for a rack bearing is disclosed by Piotrowski et al. in U.S. Pat. Pub. No. 2005/0126328 A1 entitled RACK AND PINION STEERING GEAR ADJUSTER CLEARANCE ENHANCEMENT, the disclosure of which is hereby incorporated herein.
An improved steering gear assembly that inhibits the development of rattle as the rack and pinion are subjected to wear, is desirable.